The effect of p-GaN : Mg layers on the turn-on voltage of p-n junction LED

We have studied the effect of p-GaN:Mg cap layers which were grown using MO CVD with various flow rates of Cp2Mg on the turn-on voltage of p-n junction LED. Before fabricating the LEDs, the p-GaN:Mg/sapphire (0 0 0 1) epilayer s grown with various flow rates of Cp2Mg were evaluated in order to investi gate the characteritics of each layer. We investigated the dependence of ac ceptor concentration on the flow rate of dopant source. The Van der Pauw te chnique, double crystal X-ray diffractometry (DCXRD:) and photoluminescence (PL) were used to characterize their crystallographic, electrical and opti cal properties. As the incorporation of Mg in GaN/sapphire (0 0 0 1) epitax y increases, the resistivity of the epilayers increases abruptly without di scontinuity due to the increase of the much uncracked Mg-H complex. In spit e of the continuous increase of Mg incorporation, the hole concentration of the epilayers increases at first and then decreases from a certain amount of Mg incorporation. As a result of the increase of the hole concentration, the emission intensity of the layers in the :PL spectra at room temperatur e increases at first and then decreases from a certain flow rate of Cp2Mg. After full evaluation of each p-GaN:Mg epitaxial layer, LED structures of t he p-n junction type were grown by the growth of these cap layers and fabri cated. Next, they were characterized by I-V measurement in order to investi gate the effect of p-GaN : Mg cap layers on the turn-on voltage of the LED structures. The current of the LEDs at forward bias mode becomes low as the resistivity of p-GaN : Mg cap layer increases. However, the LED fabricated by the cap layer which has the highest hole concentration shows the greate st current value. While the turn-on voltage of pn junction LED fabricated b y p-GaN:Mg having high hole concentration above 1 x 10(17)/cm(3) depends on the hole concentration of each p-GaN:Mg cap layer, the voltage of the devi ces fabricated by the cap layer having low hole concentration below 1 x 10( 17)/cm(3) is nearly dependent on the electrical resistivities of each p-GaN :Mg. (C) 2001 Elsevier Science B.V.. All rights reserved.